amount, the precipitate is first washed by decantation, and then collected
on a tared, or preferably a double counter-poised filter, where it is
further washed, dried at 100 deg. to 105 deg. C., and weighed. The precipitate and
filter paper are then ignited separately in porcelain, at a low red heat,
the residues moistened with a few drops of nitric acid and reignited; the
weight of the lead oxide deducted from that of the original precipitate
gives the weight of the organic matter precipitated by the lead. Raw
glycerines contain from 0.5 to 1.0 per cent.

~Albuminous Matters.~ An approximate determination of the albuminous
matters may be made by precipitating with basic lead acetate as already
described, and determining the nitrogen by the Kjeldahl method; the
nitrogen multiplied by 6.25 gives the amount of albuminous matter in the
precipitate.

~The Determination of Glycerine.~ The acetin method of Benedikt and Canton
depends upon the conversion of glycerine into triacetin, and the
saponification of the latter, and reduces the estimation of glycerine to
an acidmetric method. About 1.5 grm. of crude glycerine is heated to
boiling with 7 grms. of acetic anhydride, and 3 to 4 grms. of anhydrous
sodium acetate, under an upright condenser for one and a half hours. After
cooling, 50 c.c. of water are added, and the mixture heated until all the
triacetin has dissolved. The liquid is then filtered into a large flask,
the residue on the filter is well washed with water, the filtrate quite
cooled, phenolphthalein is added and the fluid exactly neutralised with a
dilute (2 to 3 per cent.) solution of alkali. Twenty-five c.c. of a 10 per
cent. caustic soda solution, which must be accurately standardised upon
normal acid, are then pipetted into the liquid, which is heated to boiling
for ten minutes to saponify the triacetin, and the excess of alkali is
then titrated back with normal acid. One c.c. of normal acid corresponds
to .03067 grm. of glycerine.

~Precautions.~--The heating must be done with a reflux condenser, the
triacetin being somewhat volatile. The sodium acetate used must be quite
anhydrous, or the conversion of the glycerine to triacetyl is imperfect.
Triacetin in contact with water gradually decomposes. After acetylation is
complete, therefore, the operations must be conducted as rapidly as
possible. It is necessary to neutralise the free acetic acid very
cautiously, and with rapid agitation, so that the alkali m